In manufacturing an electronic device, such as a semiconductor device, a reduction projection exposure apparatus, which reduction-projects a circuit pattern formed on a reticle (original plate) onto a wafer (substrate) coated with a photosensitive material (resist) to form a latent image pattern on the photosensitive agent, is applied.
In recent years, the mainstream of an exposure apparatus is a scanning exposure apparatus (scanner) as an improved product of a stationary exposure apparatus (stepper), which executes full-plate exposure of a reticle pattern for a shot region. The scanning exposure apparatus drives by scanning a reticle and a wafer with respect to an exposure beam formed into a slit shape through a slit to transfer a circuit pattern of the entire reticle onto the wafer. Since the stationary exposure apparatus executes full plate exposure for the shot region, it is difficult for this apparatus to perform focus/tilt correction within the shot. However, since the scanning exposure apparatus executes scanning exposure, it can follow a variation in local surface shape within the shot. This has a merit of averaging distortion in the scanning direction of a projection optical system.
As the degree of integration of semiconductor devices increases, a projection optical system of an exposure apparatus is demanded to realize a higher resolving power. In order to satisfy this demand, the wavelength λ of an exposure beam for use must be shortened, or the numerical aperture NA must be increased. The resolution is given by k1·λ/NA (k1 is a process constant). A higher resolution requires highly accurate focusing. The focus margin {d=k2·λ/NA2} becomes smaller year by year, and additionally, severe demands are imposed on components associated with focusing.
Typical factors of defocus caused in scanning exposure can be, for example, (1) a pattern offset measurement error which occurs due to a wafer having an asymmetric shape, such as a thickness variation or poor reproducibility in stage scanning, (2) a correction residue for an environmental factor, such as air fluctuations, a variation in air pressure, or a temperature variation, (3) a temporal variation in a measurement optical system, and (4) a correction residue for the lens aberration or exposure history due to exposure heat.
Three planes, i.e., the image plane (this image plane will also be referred to as the lens image plane hereinafter), in which a projection optical system forms a reticle image, the track plane (this scanning plane will also be referred to as the stage scanning plane hereinafter) of a predetermined portion (typically, the surface of a wafer chuck) of a moving wafer stage, and the reference plane (this reference plane will also be referred to as the OPTF reference plane hereinafter) of a compound-eyed focus sensor in an oblique incidence measurement optical system, which measures the focusing direction (Z direction) are not kept parallel to each other. This is a primary factor, which induces defocus in exposure.
The stage scanning plane largely varies upon reset, and its reproducibility decreases, so calibration must be performed so as to set the stage scanning plane parallel to the lens image plane or OPTF reference plane in reset. The variation in stage scanning plane upon reset is caused because the origin reproduction position of the stage is hard to stabilize. As the stage scanning plane varies upon reset, the stage scanning plane is set without being parallel to the lens image plane or OPTF reference plane.
Japanese Patent Laid-Open No. 2001-15422 discloses a technique for correcting the track of a stage driven along a polynomial surface of an N order function to the scanning plane expressed by linear components (plane). To cope with this, the amount of change in stage position in the focusing direction upon driving the stage is measured in advance to generate a correction table, thereby calculating the stage scanning plane with reference to the correction table. In the technique disclosed in Japanese Patent Laid-Open No. 2001-15422, in measurement for correction table generation, a wafer is arranged on the stage to measure the position of the wafer plane in the Z-axis direction.